The technical scope of the invention is that of pressure control valves for tanks.
The purpose of these valves is to allow the decontainment of tanks or containers containing explosive or inflammable fluids, such decontainment being necessary notably during fires. They are, for example, used in the automobile or aeronautic field to avoid excessive pressure build-up inside the fuel tank. Such pressure build-up resulting, for example, in a temperature build-up during a fire that could cause the tank to explode.
Valves are already known that comprise a flap obturating an aperture linking the inside to the outside of the tank. The flap is held in its obturating position by means of a spring.
When the pressure inside the tank exceeds a certain level (that depends on the spring""s taring force) the flap opens thereby reducing the pressure inside the tank. Overpressure due, for example, to limited over-heating caused by meteorological conditions is thus avoided.
The drawback of such a system lies in that it is not able to react quickly enough to a sudden increase in pressure such as could be caused by a fire.
Emergency defueling devices are also known, for example by patent FR2764862, in which a tank wall is pyrotechnically cut open to release its fuel content.
These devices are both cumbersome and costly and do not allow the minor overpressures that occur during normal operation to be reduced.
Valves are known, notably by patents EP766028, U.S. Pat. No. 3618627 and DE530601, in which the melting of a support means ensures the release of the flap support spring.
The drawback of these devices lies in the time required for the support means to melt.
The aim of the present invention is to propose a valve that overcomes such drawbacks.
Thus, the invention proposes a valve of simple and inexpensive design that overcomes both the moderate variations in pressure that appear during normal conditions of operation as well as the strong variations linked to abnormal environments (fire, seisms). Additionally, the valve according to the invention can adopt its decontainment position very rapidly.
Thus, the invention relates to a pressure control valve for a tank intended to contain a fluid and comprising at least one flap obturating an aperture linking the inside and the outside of the tank, such flap being held in the obturating position by spring means pressing on a support, such valve incorporating means allowing the retraction in whole or in part of the spring support such as to reduce the pressure exerted by the spring on the flap, such valve characterised in that the support has an embrittled part able to be fractured by a mobile piston activated by a pyrotechnic gas generator.
The support can be constituted by a tubular element on which a ring-shaped incipient fracture will be arranged that thus delimits the embrittled part on which the spring means press, said piston being integral with this embrittled part and having a direction of displacement substantially perpendicular to the axis of the tubular element.
The support can be advantageously displaced with respect to the body (for example by screwing) such as to regulate the value of the taring force exerted by the spring on the flap.
The piston can be substantially cylindrical in shape and can incorporate a drill-hole perpendicular to the piston axis and inside which the tubular element penetrates.
The piston can incorporate a shoulder onto which the pyrotechnically-generated gases will exert their pressure.
According to one variant, the piston can incorporate a firing pin intended to strike a pyrotechnic signalling device.
The pyrotechnic gas generator can be activated by electronic control means connected to at least one temperature and/or shock and/or pressure sensor.